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Control of residual oxygen of the process atmosphere during laser-powder bed fusion processing of Ti-6Al-4V
Additive Manufacturing ( IF 11.0 ) Pub Date : 2020-12-13 , DOI: 10.1016/j.addma.2020.101765
C. Pauzon , K. Dietrich , P. Forêt , S. Dubiez-Le Goff , E. Hryha , G. Witt

The effect of the residual oxygen concentration in the process atmosphere during laser-powder bed fusion (L-PBF) of Ti-6Al-4V was investigated, using an external oxygen monitoring system equipped with two types of oxygen sensors typically used in L-PBF hardware: a lambda probe and an electrochemical oxygen sensor. The recordings of the oxygen variations during L-PBF highlighted that the electrochemical sensor is more reliable than the lambda probe, whose signal showed a maximum deviation of about 700 ppm O2 after 7 h, attributed to its sensitivity to hydrogen present in the system. The study revealed that proper monitoring of the oxygen in the laboratory scale L-PBF system used is necessary to limit oxygen and nitrogen pick-ups by the built material. Concentrations as high as 2200 ppm O2 and 500 ppm N2 in the Ti-6Al-4V part built under standard conditions were measured, compared to maximum levels of 1800 ppm O2 and 250 ppm N2 with the external oxygen control. In addition, the findings underline the critical effect of the component design, such as the high aspect ratio columns or the lattice structures, on the heat accumulation in case of Ti-6Al-4V, leading to enhanced oxygen and nitrogen pick-up, as high as 600 ppm O2 and 150 ppm N2 difference between the bottom and top of the cylindrical samples of 70 mm height used in this study. The determination of tensile properties of samples built at different heights put in evidence the detrimental effect of the oxygen increase with build height on the ductility, which decreased from 12% to below 6% between the bottom and top positions. This work highlights that the possible presence of impurities in the L-PBF atmosphere can have harmful impact on the properties of Ti-6Al-4V components, which can be mitigated adjusting the oxygen control system.



中文翻译:

Ti-6Al-4V激光粉床熔合过程中工艺气氛中残余氧的控制

使用配备有通常在L -PBF中使用的两种氧气传感器的外部氧气监测系统,研究了Ti-6Al-4V的激光粉床熔合(L -PBF)过程中工艺气氛中残余氧气浓度的影响。硬件:λ探针和电化学氧传感器。在L -PBF期间氧气变化的记录突出表明,电化学传感器比Lambda探头更可靠,该探头的信号在7 h后显示最大偏差约为700 ppm O 2,这归因于其对系统中存在的氢的敏感性。研究表明,在实验室规模L中适当监测氧气-必须使用PBF系统来限制建筑材料对氧气和氮气的吸收。在标准条件下制造的Ti-6Al-4V部件中,测得的最高浓度为2200 ppm O 2和500 ppm N 2,而外部氧气控制的最高浓度为1800 ppm O 2和250 ppm N 2。此外,研究结果强调了零件设计(例如高长宽比的圆柱或晶格结构)对Ti-6Al-4V情况下的热量累积的关键影响,从而导致氧和氮的吸收增加,例如高达600 ppm O 2和150 ppm N 2本研究中使用的70 mm高的圆柱形样品的底部和顶部之间的差异。确定在不同高度构建的样品的拉伸性能表明,氧气随着构建高度的增加而对延展性产生不利影响,在底部和顶部之间,氧气从12%降至6%以下。这项工作强调了L -PBF气氛中可能存在的杂质会对Ti-6Al-4V组件的性能产生有害影响,可以通过调节氧气控制系统来减轻这种影响。

更新日期:2020-12-28
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